In the field of microfabrication represented by fabrication of IC chips, miniaturization of the design rules is rapidly progressing in order to achieve higher integration of the circuits. Development of a lithographic process enabling microfabrication in a stable manner has been actively pursued. However, since it has been difficult to form micro patterns of less than 45 nm with high precision by a general method of using a KrF or an ArF excimer laser, a method of using EB or EUV has been proposed.
The following various radiation-sensitive resin compositions have been proposed as positive-tone resists for electron beams or extreme ultraviolet radiation used for such ultra-microfabrication.
(1) Chemically-amplified radiation-sensitive resin composition comprising a polyhydroxystyrene resin partially protected by an acid-dissociable functional group (resin for KrF excimer), a novolak (resin for i lines), and an acid-dissociable group:
Various patent applications such as a composition containing a polyhydroxystyrene resin partially protected by an acetal group and an acid generator having well-balanced sensitivity and resolution (see Patent Document 3), a composition containing polyhydroxystyrene resin partially protected by various acid dissociable groups, an onium salt which generates a fluorine-containing aromatic sulfonic acid, and a fluorine-containing or silicon-containing surfactant (see Patent Document 4), an onium salt having at least one electron attractive group (fluorine, a cyano group, a nitro group) as a substituent of a cation moiety (see Patent Document 5), a resin having a disulfonyl group (see Patent Document 6), a resin having N-oxyimidesulfonyl group (see Patent Document 7), and the like have been disclosed. However, these methods still have not reached a practical use level in surface roughness, sensitivity, and resolution during micro-pattern formation.
Micro-pattern formation is said to be difficult when using a chemically amplified resist utilizing an effect of acid diffusion (Nonpatent Document 1).
(2) PMMA (polymethylmethacrylate) main chain cutting-type radiation-sensitive resin composition:
The resin composition exhibits excellent resolution, but can be used in practice only with difficulty due to problems of sensitivity and outgassing. Poly-t-butyl-α-chloromethylstyrene exhibiting excellent balance of resolution and sensitivity (Patent Document 1) and a resin with an atom (N, O, S) which is easily cut by electron beams introduced into the resin terminal (Patent Document 2) have been disclosed. However, although some improvement of sensitivity may be recognized, the resins still have problems in sensitivity, etching resistance, and outgassing. These resins therefore have not yet reached a practical usable level.    Patent Document 1: JP-A-2000-147777    Patent Document 2: JP-A-11-29612    Patent Document 3: JP-A-6-194842    Patent Document 4: JP-A-2000-187330    Patent Document 5: JP-A-2001-075283    Patent Document 6: JP-A-2002-072483    Patent Document 7: JP-A-2002-107920    Nonpatent Document 1: “Relation between spatial resolution and reaction mechanism of chemically amplified resists for electron beam lithography”, Journal of Vacuum Science & Technology B (USA), December, 2003, Vol. 21, No. 6, pp. 3149 to 3152